This disclosure pertains to a method for converting an aromatic aldehyde or a mixture of aromatic aldehydes to an aromatic acyl halide or a mixture of aromatic acyl halides.
Methods for converting an aromatic aldehyde to aromatic acyl halide are known in the art. For instance, in U.S. Pat. No. 3,274,242 the preparation of aromatic acyl chlorides by vapor phase chlorination of aromatic aldehydes is described at temperatures of 225° C. or higher. This method has the disadvantage that high temperatures must be used, which makes the process expensive, and for terephthaldehyde (TPAL) only a low yield was obtained.
In BE 647037, a method is disclosed wherein neat chloro-substituted aromatic aldehydes were brought in contact with chlorine gas at moderate temperatures. This method only worked for chloro-substituted aromatic aldehydes and rendered yields around 80%.
In U.S. Pat. No. 3,894,923, the conversion to benzoyl chloride is described by chlorinating neat liquid benzaldehyde using UV light and/or peroxides as catalyst. This method was only claimed for the conversion of benzaldehyde to benzoyl chloride.
In U.S. Pat. No. 2,791,608, phthaloyl chloride is prepared from oxidation of xylene in the presence of an oxidation catalyst followed by chlorination of the oxidation product. Inert solvents may be used, including aromatic dicarbocylic acid chlorides. The reaction mixture may contain toluic acids, phthalic acids, methyl and carboxy benzaldehydes, and methylbenzyl toluates. This preparation method has several disadvantages. Part of the product will be ring chlorinated due to the presence of oxidation catalysts. Accurate control of the equimolarity of methyl and acid groups in the mixture is essential. Any unbalance in the presence of these functional groups will lead to formation of significant amounts of side products that are difficult to remove from the reaction mixture. Furthermore, it is also required to remove water that is formed during oxidation to avoid formation of side products during the chlorination step. Finally, the complexity of the method, comprising oxidation, chlorination and fusion steps, is disadvantageous as well.
A method for making terephthaloyldichloride (TDC) from an aromatic aldehyde is disclosed in U.S. Pat. No. 3,950,414, wherein the preparation of aromatic diacyl chlorides is described by chlorination of aromatic dialdehydes in an inert solvent, such as carbon tetrachloride or another fully halogenated aliphatic hydrocarbon.
TPAL is converted by reaction with chlorine in carbon tetrachloride (CTC) as a solvent in high yields at moderate temperatures. According to this method TPAL can be moderately dissolved in CTC at temperatures of about 35° C., and can be chlorinated with high conversion and high selectivity by subjecting the solution or slurry to chlorine gas. The reaction rate, conversion, and selectivity of the reaction are not influenced by the presence of light. The reaction goes perfectly well in complete darkness.
However, due to more stringent environmental requirements, the use of carbon tetrachloride and other halogenated aliphatic hydrocarbons is no longer acceptable, and industrial processes using this solvent no longer can count on governmental license due to the solvent's detrimental effects on the ozone layer. Therefore a process having similar high yields and selectivity, whereas the reaction conditions in teams of reaction time and reaction temperature are equally favorable, as processes using aliphatic hydrocarbon solvents are desired.
According to the present disclosure it has now been found that TPAL can be converted to TDC under similar reaction conditions giving similar yields and selectivity, without using toxic halogenated solvents. It was also found that the present method could advantageously be used for other aromatic aldehydes as well.